High frequency antenna system



y 1943- w. H. NEWBOLD 2,318,516

HIGH FREQUENCY ANTENNA SYSTEM Filed Dec. 14, 1940 4 Sheets-Sheet l May4, 1943. w. H. NEWBOLD 2,318,516

HIGH FREQUENCY ANTENNA SYSTEM Filed Dec. 14, 1940 4 Sheets-Sheet 2 May4, 1943.

LH.NEWBOLD HIGH FREQUENCY ANTENNA SYSTEM 4 Sheets-Sheet 5 Filed Dec. 14,1940 May 4, 1943. w. H. NEWBOLD 2,318,515

HIGH FREQUENCY ANTENNA SYSTEM Filed Dec. 14, 1940 4 Sheets-Sheet 4'--.....i.---n......,.-...w

Patented May 4, i943 UNHTE HIGH FREQUENCY ANTENNA SYSTEM William H.Newbold, Langhorne, Pa", assig'nor to Philco Radio and TelevisionCorporation, Philadelphia, Pa., a corporation of Delaware ApplicationDecember 14, 1940, Serial No. 370,213

19 Claims.

This invention relates to antenna or signal collecting systems, and moreparticularly to directive antenna systems for the reception of signalsof high frequencies of the order for example of those presently employedin television transmission, and to antenna systems which aresufficiently small to be contained in the cabinet which houses the otherapparatus customarily used in receiving such signals and rendering themsensibly perceptible.

It has been the general practice prior to this invention to use, inconjunction with television receivers, elaborate outdoor antenna systemsconnected to the receiving equipment through a transmission line of fromtwenty to thirty feet or even more in length. For example one form ofsuch antenna consists of a half-wave dipole disposed upon the roof of orproximate to the dwelling house or other building in which the receiveris located and connected to the receiver by means of a length oftwisted-pair transmission line. Such an antenna has numerousdisadvantages, not the least of which are that its structure isobtrusive and unsightly to such an ex-" tent as to detract greatly fromthe appearance of the premises upon which it is located and also thatthe cost of erecting the structure is large by comparison with the costof the receiving apparatus itself, ranging usually from fifty to onehundred dollars for a single installation.

Such antenna systems have the further disadvantage that, although theymay be adjusted at the time of installation for most favorable receptionof a single station, they cannot thereafter readily be readjusted inorder to obtain optimum reception from another and differently locatedstation. For the same reason advantage cannot be taken of thedirectional properties of such a system to minimize the efiect ofinterfering sources such for example as diathermy machines and the likewhich have been found to have a particularly deleterious effect upontelevision transmissions.

Accordingly it is one object of the present invention to provideanefficient high frequency antenna system in which the antenna is ofsufficiently small overall dimensions to permit it to be included withina cabinet such as is customarily used to house the receiving equipmentin conjunction with which the antenna is to be used, thus avoiding thedisadvantages of the large outdoor antennas heretofore used in respectof both unsightliness and high cost of installation.

Another object of the invention is to provide a directional receivingantenna system adapted to be employed for the reception of highfrequency signals such as those used in television transmission, anddisposed within the cabinet housing the receiving equipment so as to bereadily controllable by the person using such equipmerit in order toobtain optimum reception of any one of a. plurality of stations and inorder to permit the elimination of the efifect upon the receiver ofinterference from sources such as diathermy machines and the like.

Still another object of the invention is to provide a high frequencyreceiving antenna system adapted tobe tunable to any one of a group ofchannels of substantially the same band-width and to be tuned in eachcase so that the band which the system is adapted to transmit is notappreciably changed in tuning from channel to channel and correspondssubstantially to the width of the band of frequencies to be received ineach channel.

Other objects and advantages will be pointed out in the course of theexplanation of a specific embodiment of the invention and certainvariations thereof. Although the scope of the invention will beunderstood to be subject only to the limitations imposed by the appendedclaims, the specific embodiment above mentioned, both as to itsorganization and mode of operation will best be understood by referenceto the following description and the accompanying drawings in which:

Figure 1 is a schematic circuit diagram illustrating one embodiment ofthe invention and certain of its variations;

Fig. 2 is a. rear view in perspective of the cabinet housing atelevision receiver and a directional loop antenna system in accordancewith the invention;

Fig. 3 is a detailed perspective view showing the structure of ashielded loop antenna for use in a circuit in accordance with theinvention;

Fig. 4 is a detailed perspective view showing the structure of a dipoleantenna for use in a circuit in accordance with the inventiony Fig. 5 isa perspective view showing a loop antenna of the kind shown in Fig. 2mounted in the cabinet housing a television receiver so as to berotatable about horizontal as well as vertical axes, whereby the planeof the loop may be oriented for the optimum reception of signals in' anydirection;

Fig. 6 is a detailed cross sectional view showing the support, bearingand pulley structure used in the arrangement of Fig. 5;

.Fig. '7 is a detailed view showing the bearing of one form of each ofthese types of signal collector will be set forth more fullyhereinafter. Sufilce it for the present to say that either issufflciently small in respect to its physical dimensions to be containedwithin the cabinet which houses other receiving equipment. In everycase,

therefore, the effective length of either the dipole or the loop will beless than one-half wave length of the highest frequency at which thesystem is adapted to operate. Practically, of course, it will beunderstood that either one and not both of sired band of frequencies ineach channel. Thi will be explained more fully hereinafter.

The circumstances which permit, and the ad vantages to be derived fromtuning the antennl circuit in the system just described will now b setforth. First itis to be noted that in the can these signal collectorswill be used in a given reas for example coaxial. or open wire lineswhich would introduce less loss. However the twisted pair line hasproven entirely satisfactory in most embodiments. The other end of theline is connected to two terminals of each of aplurality.

of triple gang switches 5, 6, I, and 8. The third terminal of each ofthe said switches may be connected to the grid of a space discharge tube9 through a coupling condenser l and grid leak. II. The tube 9represents any suitable means adapted to utilize the signal collected bythe dipole l or the loop 2, depending upon which is used, and may forexample be a radio frequency amplifier or a frequency converter tube ina television receiver or the like. The power supply and output circuitsof this tube have not been shown inasmuch as they do not materiallyinfluence the operation of the circuit which is the subject of theinvention. It will be understood that this tube may be followed by theusual circuits employed in a television or other receiver of highfrequency signals.

The operation of any one of the switches 5, 6, v

1, or 8 will serve to connect between the free end of the transmissionline 4 and one'side of the coupling condenser l0 one of the antennacoupling transformers l2, l3, I4 or I 5 and additional tuning means inthe primary circuits thereof :adapted to modify the effective length andcharacteristics of the transmission line section 4 whereby the antennacircuit is adapted to be tuned to receive signals in a particularchannel.

This additional tuning means may consist either of a further section oftransmission line as shown at It or of lumped reactive elements such asof the half-wave dipole antenna it is impossibll to tune the antennacircuit for relatively narrow band response to signals within a singlechannel This is due to the low value of 'Q inherent in suci an antennawhich, in fact, is such as to permi' its use over a wide range offrequencies to rcceivl signalsin a number of different channels. For ex-"ample it. has been customary to use a single dipoli antenna forreceivingsignals in several diiferen channels located in thefrequency/range from 5( to loakmegacycles used for television. Since thrantenna is not tuned-it obviously cannot pick u: all signals withoptimum efliciency.

Ithas beenffound that the use of an antenna of relatively smallerdimensions not only permits the inclusion thereof within the cabinei"housing the-other receiving equipment, but ii likewise permits theantenna circuit to be tuned sons to give a substantially uniformresponse over} a relatively narrow but suillciently' wide bandoffrequencies. This is by reasonof the I fact that the smaller antennacan be constructed those shown at l1 and I 8. For one channel the'primary circuit'is adapted to be tuned solely by means of thetransmission line 4 as shown at l9 and without the use of any additionaltuning means. The transformer secondary circuits are likewise tuned to afrequency within the channel to be received, and since this can inostreadily be done by designing the transformer so that the inductanceappearin across its secondary terminals resonates with the inputcapacity of the following amplifier stage at the desired frequency, ithas been found convenient to provide a separate transformer for eachchannel to be received. The primary and secondary circuits of theseveral transformers are tuned in accordance with wellknown principlesapplicable to tuned coupled circuits to give the required response-overthe deso as-to have a relatively high value of Q. In other words,considering the problem from-the viewpoint of the theory of coupledcircuits, ii is necessary to provide sumcient damping in eithertheprimary or secondary circuits orboth to give the'required bandwidth.With a large antenna more damping is provided by the antenna alone thanis required to give the desired band width for a single six megacycietelevision channel. However in the case of a small antenna the value ofQ may be made such as to provide the necessary damping for a sixmegacycle channel. Although additional damping may be added to give thedesired band width, it is preferable to construct the antenna so thatsubstantially the entire primary circuit resistance is the radiationresistance of the antenna, since when this condition obtains, theantenna will operate at maximum emciency. In constructing the antennawith this end in view it should be remembered that in the case of theloop, increasing the area thereof increases theradiation resistance,while increasing the diameter of the conductor of which the loop isformed decreases its inductance. Likewise in the case of the dipole,increasing its length increases its radiation resistance, while theaddition of capacitive loading at the ends of the dipole decrease thecapacitive reactance, In general therefore it will be desirable to makethe loop or dipole as large as is permissible in view of the availablespace in the cabinet and then to make the diameter of the loop conductoror the loading of the dipole just sumcient to give the desired value ofQ.

It should also be pointed out that the bandwidth will be somewhataffected by the length of the transmission line connecting the antennato the transformer primary. In general the effect of using a greaterlength of transmission line between the antenna and the transformer willbe to produce a more sharply resonant primary circuit than when ashorter length of line is used. Since the transmission line section 4 inFig. 1 is always connected inthe primary circuit regardless of whichtransformer is in use, this section should be chosen of such length aswill cooperate with the antenna to give the desired band width. This,however, is not the only consideration involved in the choice, for theline must be of sumcient length at least to tune the primary circuit.

In the case of a loop antenna it will ,be desirable to have theeifective electrical length of the circuit including the antenna, thetransmission line 4, the tuning means, and the "primary winding of thetransformer substantially equal to.

electrical "distance" from the midpoint of the loop or the tips of thedipole to the midpoint of the transformer primary. This, of course, isonly one-half the electrical distance around the complete circuit but,for the purposes of this specification and the appended claims, it willbe convenient to adopt this definition. In the case oi the loop thiswill make the midpoint of the loop conductor and the center point on thetransformer primary winding voltage nodal points. If the eilectiveelectrical length of the loop antenna is less than one quarterwavelength, as is the case in the embodiment herein described, thevoltage maximum point of the circuit will be somewhere along thetransmission line 4, for example at the point 32-32 as indicated inFig. 1. In thisgcase all points on the antenna will be at relatively lowpotentials and shielding problems will be considerably simplified. Itwill be found that capacitive pickup by the loop, which has anundesirable effect upon its directional characteristics and shouldtherefore be avoided, may be reduced to a satisfactory minimum by usinga transmission line comparatively free from capacitive pickup, such asaby using an electrostatic screen surrounding at least those portions ofthe loop which are at high potential. The structure of the screen whichmay be used will be discussed in more detail when consideration ishereinafter given to the structure of the loop.

When an antenna in the form of a dipole is used, the electrical lengthof which is less than one-quarter wave-length it will be desirable toemploy a sumcient length of line to render the overall electrical lengthof the circuit equal to a quarter wave-length. Then the ends of thedipole elements will be at maximum potential and the voltage node willagain obtain in the transformer primary. Of course, if the length of thetransmission line necessary to make the electrical length of the circuitone-quarter wavelength is not suflicient to span the distance betweenthe antenna and the switching means, a

longer section may be used which may be such as will make the circuit anodd number (three for example) of quarter waves in length. Howeverconsideration must be given to the fact that as the length of the lineis increased, its resonances tend to become sharper and may have anundesirable effect upon the width of the frequency band which thecircuit will transmit. This sharpening may to some extent be compensatedfor by increasing the dissipation of the line or by adding resistanceexternally. The same considerations apply in the case where a loopantenna is employed and a length of transmission line is used such aswill make the circuit of electrical length equal to an integral numberof half wave-lengths greater than one.

In general it is desirable to use as short a length of line as willconveniently connect the antenna to the primary terminals of thetransformer and provide the desired tuning. In the tuning process, ofcourse, the effective electrical length of this line will be keptsubstantially constant and in consequence of this, as the tuning of the"circuit is varied from onechannel to another,

the band-width will remain substantially constant. e

As hereinbefore indicated in the general discussion of the embodiment ofthe invention shown in Fig. 1, a plurality of tuning means are providedfor connecting the end of the transmission line 4 to the primarywindings of the transformers l2, i3, i6 and i5. By these means theeflective electrical length of the transmission line 4 may be varied totune the several primary circuits to different frequencies for thereception of signals in different channels. Such tuning. means mayconsist either of additional lengths of transmission line or of lumpedreactive elements capable of modifying the effecf tive length of theline. Referring, for example, to Fig. 1 there is shown a length oftransmission line l6 which by operation of the switch 5 may be connectedbetween the free end 20 of the transmission line 4 and the primary ofthe transformer II. If, for example, when the switch 5 is closed toconnect the end 20 of the line 6 directly to the primary winding of thetransformer It, the circuit including the antenna, the line 4 and theprimary of the transformer i3, is tuned to a frequency f1, then the linesection l8 may be made of such length that it will tune the circuitincluding the antenna, the line 4 and the primary of the transformer l2to a frequency is which may be either higher or lower than ii. Thelength of line required to change the tuning from a given frequency 11to another frequency is will differ depending upon whether a loopantenna or a dipole antenna is used. If at the frequency h to which theprimary circuit is tuned by the line 4 alone, the efl'ective electricallength of the entire circuit including the antenna. the line 4 and theprimary of the transformer is lo centimeters and if the effectiveelectrical length of the additional line section It is l centimeters.the circuit including the additional line section will. in the case ofthe loop, be an integral number of half waves in length at any frequencyf2 given by the expression:

odd number of quarter waves in length at any frequency f2 given by theexpression and the primary winding of the transformer M- Here the sameresults obtain regardless of the primary circuit so as to tune it to ahigher frequency than that to which it would be tuned in their absence.It will be apparent that series I inductors might be employed in asimilar man ner effectively to lengthen the primary circuit electricallyso as to tune it to a lower frequency.

The switch 8 is adapted upon being closed to connect the condenser l8 inshunt across the end of the transmission line 4 and the primary of thetransformer I5. The condenser when thus connected acts effectively tolengthen the primary circuit and to tune it to a lower frequency. In thesame manner, of course, a shunt connected inductor would operate toshorten the eifective electrical length of the circuit and to tune it toa higher frequency.

It will of course ,be understood that the alternative methods justdescribed for tuning the primary circuits of the four transformers I2,l3, l4 and IS in the system of Fig. 1 are merely exemplary and that anydesired number of circuits may be incorporated in a particular receivereach tuned by any of the aforementioned methods in order to permit thereception at will of any one of a number of channels corresponding tothe number of such circuits provided.

It is also to be pointed out with reference to Fig. 1 that means may beprovided at the point of connection of the antenna to the transmissionline 4 for separately tuning the antenna apart from the several couplingcircuits. For example there are shown adjustable condensers 2| connectedserially in the leadsto the dipole I and an adjustable condenser 22connected serially in the loop circuit 2. Alternatively of courseadjustable inductances might be used for the same purpose and theelements in either case might be connected either in shunt across theleads from the dipole or serially in the loop leads, though thearrangements as shown are preferred. By such tuning it is possibleeflectivelyto modify the electrical length of the circuit comprising theantenna and the line section 4 for all frequencies at which the systemis intended to be operated. Such an adjustment is equivalent in effectto changing the effective length of the line section 4 and may be reliedupon as a convenient means for accomplishing this end.

Referring now to Fig. 2 there is illustrated an arrangement of arotatable loop antenna disposed within the cabinet of a televisionreceiver and adapted to be used in conjunction with the circuits abovedescribed. The loop 23 in this embodiment may comprise a rectanglesixteen inches on each sideformed of a single length of threeeighthsinch copper tubing, which was found to havethe requiredvalue ofradiation resistance to yield the desired six megacycle bandwidth inaccordance with the principles already set forth.

It may conveniently be supported by clamping between two verticalmembers 24 and 25 of wood or like insulating material. The verticalmember 22 is provided at each of its ends with metal bearing pins 28 and21 ,(see' Fig. 3). Said pins are adapted to be journaled in bearings orany satisfactory form in the shelf 28 and baseboard 29 within cabinet 30in which are also arranged the other components SI of a televisionreceiver. Pinned or otherwise amxed to the lower bearing pin is a pulleywheel "32 for rotating the loop. The other apparatus for effecting suchrotation may comprise the pulley wheels 33 and the pulley wheel 34mounted on the shaft 35 adapted to be turned by a knob 36 operable fromthe front of the cabinet. A cord or belt 31 running over all of thesepulleys permits the antenna to be rotated about its vertical axis. byturning the knob 36. Such rotation may be restricted to one complete 360turn by the cooperation of a pin 38 on pulley 32 and a stationary stop.The ends of the loop 23 are connected through the adjustable condenser22 corresponding to the like numbered element in Fig. 1. The ends of theloop are likewise connected to one end of the twisted-pair transmissionline 4, similarly identified in Fig. l, the other end of which isconnected to terminals 20. The latter terminals may be connected to theseveral switches (not shown in Fig. 2) in the manner shown in Fig. 1.The size of the loop is of course restricted only by the size of thecabinet in which it is to be included, and by reason of the fact that itis desirable that the loop should be rotatable therein in order to takeadvantage of its directional characteristics. sirable since it rectionalcharacteristics known to be inherent in such a loop antenna in excludingsignals from stations other than the one desired to be received and inexcluding all but the direct wave from the desired station.

In order to maintain the desired directional characteristic it has beenindicated that the loop may preferably be shielded to prevent electricpickup. Althoughthe shielding has been omitted in Fig. 2 for clarity, itis shown in Fig. 3 consisting of a plurality of vertically arrangedconductors 40 in planes on opposite sides of the loop. These conductorsmay conveniently be cemented in sandwich fashion between two sheets ofheavy paper 4| and 42 which may be fastened to the vertical members 24and 25 as shown in Fig. 3. The shield conductors 40 are preferablyconnected together and to a ground connection on the receivingequipment. This connec- Rotatability is particularly detion should bemade as short as is feasible so "point on the receiving equipment on theshelf 28.

As heretofore stated the fact that the maximum voltage point in theantenna circuit may be made to occur at a point on the transmission linecooperates to improve the shielding. Both this effect and the action ofthe shield Just described cooperate to render the structure a puremagnetic pickup device.

The structure of a dipole antenna for use in connection with thecircuits already described with reference to Fig. 1 is shown in Fig. 4.It comprises two horizontally disposed conductive dipole elements 44inserted in sockets in an insulating separator 45 clamped betweenvertical members 48 and 4'! similar to those employed in the case of theloop. In the embodiment shown the length of the dipole measured betweenthe extremities of the elements 44 is seventeen inches. Capacitiveloading was provided by means of plates 48 amxed to the ends of the rods44. It will be noted that each of these plates comprises three sections.Each plate was twelve inches deep, the outer sections were three andone-half inches wide; and the central section was four and permits theutilization of the difrom the innermost ends of the dipole elementsthrough the condensers 2|, also designated in the circuit diagram ofFig. 1, to the transmission line 4.

Although it has been observed that both the loop and the dipole are maderotatable about a vertical axis in order. to take advantage of theirdirectional features in tuning out undesired sig-' nals and noise,attention should be called to the fact that in order to take the utmostadvantage of these directional characteristics the loop antenna shouldbe' used where the electric waves to be received are verticallypolarized and the di-' pole where they are horizontally polarized. Ithas been found in some cases that although the waves originallytransmitted may have been either vertically or horizontally polarized,when they reach the receiver the polarization has been changed. This maybe due to the presence of a reflected wave so that the-field at anypoint may be the resultant of two or more waves some of which may be.reflected. Under such circumstances it is no longer possible to obtainoptimum reception using an antenna whose directivity is limited to,asingle plane. It is then desirable to provide an antenna rotatable inalldirections so as to be capable of optimum reception of a wave comingfrom any direction and with any polarization.

An arrangement permitting such. operation and employing a loop antennais shown in Fig. 5. Here a loop 49 is clamped between two members 50 and5| as in the embodiment of Fig. 3. It is supported. so as to berotatable about a horizontal axis by means of pins or studs, one ofwhich is shown at 52, journaled in the uprights 53 of a cradle support54. The latter is mounted upon a swivel base 55 so as to be rotatableabout a vertical axis. A system of cords and pulleys is provided bymeans of which the antenna may be oriented in any desired plane. Forthis purpose the control knobs 56 and 51 operable from the front of thecabinet are used. The stud 52 at one end of the loop supporting members50 and 5| is provided with a pulley 58, as shown more clearly in Fig. 7.The cord 59 passes around the pulley 58, over the pulleys 60 aflixed toa lower corner of the cradle 54, as shown more clearly in the detaileddrawing of Fig. 8, and then around a pulley 6| concentric with the axisof the swivel mounting 55. The latter is shown in vertical cross sectionin Fig. 6. The pulley Bl-is adapted to accommodate a second cord 62which passes over the pulleys 63 and around the pulley 64 attached tothe end of the shaft controlled by the knob 56, thereby completing thelinkage for producing rotation of the loop 49 about a horizontal axis.The pulley 65 is amxed to the shaft 55 which in turn is rigidly attachedto the cradle 54. The cord 6! passes over the pulley 65 and thence overthe pulleys 68 and around the pulley 69 aflixed to the end of the shaftcontrolled by knob 51, thereby completing the linkage for efiectingrotation .of the cradle 54 The bent structure of plates 48, as

and of the loop 49 supported therein about a vertical axis.- The entireswivel support may be afllxed to the base of the cabinet by means ofscrews I inserted through holes in the bracket II which supports theentire assembly. Attention is called to.the fact that the pulley 65 isdirectly and rigidly coupled to the cradle 54 by means of the shaft 66having a flange l: which .may be afilxed to the cradle by bolts or othersuitable means. The lower surface of the flange bears on the plate I3affixed to the bracket II by. screws, being separated therefrom by awasher 14. The pulley 6|, on the other hand, is free to rotate on thebracket II and is provided with upper and lower washers l5 and 16 tofacilitate such rotation. Electrical connections are made from theantenna to the receiving apparatus 3| through the twisted cable ,4.

Since the loop antenna just described can be orientated in any plane bysimply turning the knobs 56 and 51 it may be adjusted to the optimumreception of signals arriving from any di rection and to discriminateagainst signals arriving from other directions whereby the unde- 5sirable effects of reflections and noise may be considerably reduced.

Wherever in the foregoing specification the symbol Q has been used ithas been employed in its usual sense and signifies either the ratio ofwL/R when applied to an inductive circuit element having inductance Land series resistance R or the ratio of G/wC when applied to acapacitive circuit element having capacitance C and shunt conductance Gand where 0: represents the angular frequency at which the measurementis It will of course be understood that although the invention has beendescribed with reference to certain embodiments, it is capable ofexpression in other embodiments which will occur to those skilled in theart, and it is not intended that the invention shall be restricted inscope except by the appendedclaims.

, I claim:

. 1. In a receiving system for high frequency electromagnetic wavesignals, an antenna system having a circuit which includes an antenna, atransmission line section and the input circuit of a coupling deviceisaid circuit being tuned to receive signals in a. certain channel andbeing damped so as to have the desired band-width for the reception ofsignals in said channel only, said clamping being due principally to theradiation resistance of said antenna; a second coupling dewithin saidchannel and being damped so as to have the desired band-width for thereception of signals in said channel only, said damping being dueprincipally to the radiation resistance of said antenna} a secondcoupling device and an addltional means connectable in said circuit inplace of said first coupling device for tuning said circuit to receivesignals in a different channel without tion resistance or said antenna;a second coupling.

device and an additional section of transmission line connectable insaid circuit in place of said first coupling device for tuning saidcircuit to receive signals in a diiIerent channel without substantiallychanging said band-width.

4. In a receiving system for high frequency electromagnetic wavesignals, an antenna system having a circuit which includes an antenna, a

transmission line section and the input circuit of a coupling device,said circuit being tuned to receive signals in a certain channel andbeing damped so as to have the desired band-width for the reception ofsignals in said channel only, said damping being due principally to theradiation resistance said antenna; a second couplin device and lumpedreactive circuit elements cone nectable in said circuit in place oi saidfirst coupling device for tuning said circuit to receive signals in adiflerent channel without substantially changing said band-width.

5. In a receiving system for high frequency electromagnetic wavesignals, an antenna system having a circuit which includes an antenna, atransmission line section and the input circuit of a coupling device,said circuit being tuned to receive signals in a certain channel andbeing damped so as to have the desired band-width tor the reception ofsignals in said channel only, said damping being due principally to theradiation resistance of said antenna; a second coupling device and anadditional section oi transmission line having an eflective electricallength less than one quarter wave at a irequency within said channelconnectable in said circuit in place 01 said first coupling device fortuning said circuit to receive signals in a diiierent channel withoutsubstantially changing said band-width.

6. In a receiving system ror high frequency electromagnetic wavesignals, an antenna system having a circuit which includes an antenna, atransmission line section and the input circuit of a coupling device,said circuit being tuned to receive signals in a certain channel andbeing damped so as to have the desired band-width tor the reception ofsignals in said channel only, said damping being due principally to theradiation resistance of said antenna; a second coupling device and anadditional section oi. transmission line having an eflective electricallength greater than one quarter wave but less than one half wave at afrequency within said channel connectable in said circuit in place ofsaid first coupling device iortuningsaidcircuittoreceivesignalsinadiri'erent channel without substantially changing said band-width.

7. In a receiving system for high frequency electromagnetic wavesignals, an antenna system having a circuit which includes a loopantenna, a transmission line section and the input circuit oi a couplingdevice, said circuit. being tuned toreceivesignalsinacertainchannelandtohave an eiiective electrical length equal to an integral number 0! onehalt wave lengths at a irequency within said channel and being damped soas to have the desired band-width for the reception of signals in saidchannel only, said damping being due principally to the radiation resistance or said antenna; a second coupling device and additional meansconnectable in said circuit in place of said first coupling device iortuning said circuit to receive signals in a diiierent channel withoutsubstantially changing said band-width.

8. In a receiving system for high frequency electromagnetic signals, anantenna system having a circuit which includes a dipole antenna, atransmission line section and the input circuit cl 9, coupling device,said circuit being tuned to receive signals in a certain channel and tohave an efiective electrical length equal to an odd number of quarterwave lengths at a irequency within said channel and being damped so asto have the desired band-widthwior the reception oi. signals in saidchannel only, said damping being due principally to the radiationresistance of said antenna; a second coupling device and additionalmeans connectable in said circuit in place 01' said first couplingdevice for tuning said circuit to receive signals in a different channelwithout substantially changing said band-width.

9. In a receiving system for high frequency electromagnetic 'wavesignals, an antenna system having a circuit which includes an elec--trically shielded loop receiving antenna, a transmission line sectionand the input circuit of a coupling device, said circuit being tuned toreceive signals in a certain channel and to have an effective electricallength equal to one halt wave at a frequency within said channel, saidcircuit having a voltage maximum point located on said transmission lineand being damped so as to have the desired band-width for th receptionoi signals in said channel only, said damping being due principally tothe radiation resistance of said antenna.

10.In a receiving system for high frequency electromagnetic wavesignals, an antenna system having a circuit which includes anelectrically shielded loop receiving antenna, a transmission linesection and the input circuit or a coupling device, said loop antennabeing rotatable about a a vertical axis through the plane of said loopto tune out undesirable signals in at least one direction, and saidcircuit being tuned to receivesignalsinacertainchannelandtohaveaneiiective electrical length equal toa one half wave at a frequency within said channel, said circuit havinga voltage maximum point located on said transmission line and beingdamped so as to have the desired band-width for the reception of signalsin said channel only, said damping being due principally to theradiation resistance of said antenna.

11. m a receiving system for high frequency electromagnetic wavesignals, an antenna system entirely contained within a cabinet housingother receiving equipment comprising said receiving system, said antennasystem having a circuit which includes an antenna, a transmission linesection and the input circuit of a coupling device, said antenna havingan eii'ective electrical tuned to receivesignals in one 01' saidchannels and being damped so as to have the desired bandwidth for thereception of said signals in said channel only; a plurality or othercoupling devices and additional means alternatively connectable in placeof said first coupling device for tuning said circuit to receive signalsin others of said channels without substantially changing saidband-width.

12. In a television receiver, a built-in directional antenna system forreceiving television signals in different channels, said systemcomprising an antenna disposed within the cabinet housing said receiverand rotatable to tune out undesired signals in at least one direction, aplurality of coupling devices, a transmission line section forconnecting said antenna to one of said coupling devices, and a pluralityof means connectable in circuit between said transmission line and oneof said coupling devices, each adapted to tune said circuit to adiiferent channel without substantially changing the band-width.

13. In a television receiver, an antenna system for receiving highfrequency wave signals in different channels, said system comprising anan: tenna disposed within the cabinet housing said receiver a supportdisposed within said cabinet and rotatable about a vertical axis, asecond support carried by said first support and rotatable about ahorizontal axis, said antenna bein mounted on said second support, meansoperable at will to rotate said first support, other means operable atwill to rotate said second support relative to said first support, saidlast two means permitting said antenna to be oriented in any desiredmanner for the optimum reception of wave signals, from a given directionand for discriminating against signals from other directions, and meansfor forming in conjunction with said antenna a plurality of circuits,each tuned to a difierent channel and each being damped, said dampingbeing due principally to the radiation resistance of said antenna.

14. In a receiving system for high frequency electromagnetic wavesignals, an antenna system comprising a circuit tuned to receive signalsin a certain channel, said tuned circuit comprising a loop receivingantenna having an effective electrical length of less than one-quarterwave length,

a. transmission line whose electrical length is substantially equal tothe difference 'between the length of said antenna and an integralnumber of half wave lengths, and the input circuit of a coupling device,all directly connected in said tuned circuit, said antenna being of suchelectrical dimensions compared to the other components of said circuitthat, for the frequency to which said transmission line whose electricallength is substantially equal to the difference between the length ofsaid antenna and an odd number of quarter wave lengths, and the inputcircuit of a coupling device, said components being serially connectedand tuned as a whole largely by the presence of said transmission line.

16. In a receiving system for high frequency electromagnetic wavesignals, having a cabinet for housing said receiving apparatus, areceiving antenna disposed within said cabinet, a transmission linesection serving to connect said antenna to said receiving apparatus andbeing of electrical length commensurate with said antenna, and means forforming a plurality of tuned circuits, each tuned to a diiferentfrequency and each including as an integral part thereof said antennaand said transmission line section. 1

17. In a receiving system for high frequency electromagnetic wavesignals, having a cabinet for housing said receiving apparatus, areceiving antenna disposed within said cabinet, a transmission linesection serving to connect said antenna to said receiving apparatus andbeing of electrical length commensurate with said antenna, an adjustablereactive element connected across said transmission line at its point ofconnection to said antenna to modify the effective impedance of saidantenna, and means for forming a plurality of tuned circuits, each tunedto a plurality of circuits, each circuit being tuned to receive signalsin a different channel and each circuit being damped so as to havesubstantially the same effective band-width, said damping beingdue-principally to the radiation resistanceof said antenna.

19. In a television receiver, a built-in antenna system for receivingtelevision signals in different channels, said-system comprising anantenna disposed within the cabinet housing said re ceiver and beingrotatable in any direction for the optimum reception of wave signalsfrom any given direction and for discriminating against signals fromother directions, and means for forming in conjunction with said antennaa plurality of circuits, each circuit being tuned to receive signals ina different channel and each circuit being damped so as to havesubstantially the same effective band-width, said damping being dueprincipally to the radiation resistance of said antenna.

WILLIAM H. NEWBOLD.

